The present invention relates to controlling the drying time of ink in a hardcopy apparatus. In particular, the present invention relates to varying the time between successive passes of a printhead in a printer in dependence upon one or more printing variables.
In printers, the interswath drying time is the time the printer carriage remains (after one pass is printed) at one side of the printer before the printing of the next pass begins. This time may range between about zero and two seconds. The reason for the existence of this interswath drying time is the need for a certain amount of time for the ink to wet the print medium properly and prevent substantial mixing with or bleeding into subsequently applied ink. In the absence of an appropriate interswath drying time, solid color blocks printed next to each other may bleed and result in blurred edges. In addition, secondary color blocks may show mottled or non-uniform area fills.
Interswath drying time is conventionally complemented with an xe2x80x9cend of plotxe2x80x9d drying time, which is the time between the plot or printing task being finished and a subsequent cutting of the print media by a print media handling unit, if necessary, and deposition of a cut print media in a bin or other receptacle. The reason for this xe2x80x9cend of plotxe2x80x9d drying time is to substantially avoid the transfer of ink from the printing region to the bin, to thereby substantially avoid the possibility that the image could get blurred or stained.
However, an interswath drying time extending for a relatively long period of time may also produce problems. A problem which occurs frequently in ink-jet printing is the xe2x80x9cslewing decapxe2x80x9d effect. If the printhead has been out of its service station without firing beyond a predetermined time, the pigment in the ink may move back into its channel away from the firing chamber of the printhead. It will be appreciated that the main constituents of printer ink are an appropriately-colored pigment fraction and a more volatile vehicle fraction for conveying the pigment. If the pigment moves back into the channel, the liquid remaining in the firing chamber is basically the vehicle fraction (the first few drops of ink printed will basically have no pigment left). The result of this effect is incomplete, blank or blurred lines, or in the worst cases defective borders in images.
The defect may become worse the longer the time the printhead, otherwise known as a xe2x80x9cpenxe2x80x9d, is out of the capping position (i.e., without spitting).
Thus, there is a need to control the interswath drying time so that it is within a predetermined range of time.
One previous proposal was to determine interswath drying time only as a function of the print media used. Thus, for types of paper which needed a long drying time, a longer interswath drying time was set; whereas, for thicker and more absorbent media, a shorter drying time was set.
A disadvantage of this previous proposal was that it was relatively coarse and did not take into account various relevant factors, including stewing decap. Once set, operation of this previous proposal caused the interswath drying time to remain constant throughout a single plot.
Separate proposals have been made to overcome the problem of slewing decap. For example, the effects of slewing decap can be substantially reduced by the use of multiple pass printing. Multiple pass printing typically involves the printing of each swath in a plurality of passes, in which an appropriate fraction of the total number of dots is deposited during each pass. This technique substantially reduces the throughput of a printer because of the increased printing time necessary to perform the multiple passes. Another solution is to cause the pens to spit extensively before the swaths are printed. This increases costs due to the amount of ink wasted in the spitting process and also reduces throughput because of the time required to perform the spitting operations. U.S. Pat. No. 5,714,990 discloses an ink jet printer in which a printing operation is controlled based on the density of the image to be printed. The printing frequency of firing the ink jets is controlled to ensure that the ink jets have time to refill between swaths. A dry time per swath is calculated, and is utilized at the end of a plot when a check is made, regardless of whether any previously printed swath has had insufficient drying time to prevent smearing by an adjacent sheet.
U.S. Pat. No. 5,608,439 discloses a printing mechanism in which a swath drying time is determined in order that the printhead is not caused to smear ink in the preceding swath when printing the current swath. Thus, data concerning a just-printed swath is taken into account. In addition, look up tables are maintained for different paper sizes and print modes.
U.S. Pat. No. 4,469,026 relates to the end of plot dry time and takes into account print density, ink characteristics, humidity and temperature.
Certain aspects of the present invention seek to overcome or reduce one or more of the above problems.
According to a first aspect of the present invention, there is provided a method of reducing bleeding between ink deposited on a print medium in successive passes in a printing operation. In the method, the amount of ink deposited is determined and the drying time is varied between successive passes to keep the amount of bleeding below a predetermined level.
According to a second aspect of the invention, there is provided a hardcopy apparatus including a movable carriage carrying a printhead and a drive device arranged to advance a print medium through the apparatus. The printhead is arranged to deposit ink on the print medium in a print zone as the carriage moves in passes across the print medium. A control means is provided and arranged to vary the drying time between successive passes in dependence on the amount of ink deposited to keep the amount of bleeding between successive passes below a predetermined level.
The predetermined level may be determined solely on the basis of the ink deposited. Thus, it may be based on the previously deposited ink being substantially dry. It may also be based on the level of bleeding allowed being imperceptible to the unaided eye. It may further be based on the maximum distance which the ink is permitted to travel in the bleeding direction, i.e., transversely of the swath.
Alternatively, the predetermined level may also take into account the slewing decap effect mentioned above, so that a compromise level may be determined between the drying time being too short and too long.
According to a third aspect of the present invention, there is provided a hardcopy apparatus including a movable carriage carrying a printhead and a drive device arranged to advance a print medium through the apparatus. The printhead is arranged to deposit ink on the print medium in a print zone as the carriage moves in passes across the print medium. The apparatus also includes a detector for detecting the amount of ink I1 deposited in a preceding printing pass and/or detecting the amount of ink I2 to be deposited in a succeeding printing pass. The apparatus further includes a control device, in which the detector is connected to the control device and the control device controls the time kxe2x80x2i between successive passes in accordance with the formula
kxe2x80x2i=ki(1xe2x88x92ci(Ixe2x88x92I0))
where ki is a basic interpass drying time, which is a constant for a particular type of print media;
I is I1 or I2 or a suitable function of the two values;
I0 is reference amount of ink deposited; and
ci is a positive empirically determined constant.
According to a fourth aspect of the present invention, there is provided a hardcopy apparatus including a movable carriage carrying a printhead and a drive device arranged to advance a print medium through the apparatus. The printhead is arranged to deposit ink on the print medium in a print zone as the carriage moves in passes across the print medium. The apparatus also includes a print medium indicator, a humidity sensor for detecting the relative humidity HR, a temperature sensor for detecting the temperature T, a detector for detecting the amount of ink I1 deposited in a preceding printing pass and/or for detecting the amount of ink I2 to be deposited in a succeeding printing pass. The apparatus further includes a control device. The indicator, the sensors and the detector are connected to the control device, and the control device controls the time kxe2x80x2i between successive passes in accordance with the formula
kxe2x80x2i=ki)1xe2x88x92ai(Txe2x88x92T0)+bi(HRxe2x88x92HR0)+(+ci(Ixe2x88x92I0))
where ki is a basic interpass drying time which is a constant for a particular type of print media;
T0 is a reference temperature
HR0 is a reference relative humidity;
I is I1 or I2 or a suitable function of the two values;
I0 is reference amount of ink deposited;
and ai, bi and ci are positive empirically-determined constants.